1. Field of the Invention
The invention relates to radio frequency identification (RFID) tags, and in particular, to data retention and refresh in RFID tags.
2. Background Art
Radio frequency identification (RFID) tags are electronic devices that may be affixed to items whose presence is to be detected and/or monitored. The presence of an RFID tag, and therefore the presence of the item to which the tag is affixed, may be checked and monitored wirelessly by devices known as “readers.” Readers typically have one or more antennas transmitting radio frequency signals to which tags respond. Because the reader “interrogates” RFID tags, and receives signals back from the tags in response to the interrogation, the reader is sometimes termed as “reader interrogator” or simply “interrogator.”
With the maturation of RFID technology, efficient communication between tags and interrogators has become a key enabler in supply chain management, especially in manufacturing, shipping, and retail industries, as well as in building security installations, healthcare facilities, libraries, airports, warehouses etc.
Each tag typically stores a unique identification number and may store further data. A tag's identification number is read by a reader to uniquely identify the tag. The identification number may be stored in a non-volatile memory of the tag. It is desirable for tags to have a long shelf life, which may be 10 years or even more. Thus, for a tag to be uniquely identifiable for its lifetime, the identification number stored in the non-volatile memory may need to remain accurately stored in the memory for 10 years or more. However, even non-volatile memories can lose data over such long time periods. Thus, some tags may lose their identification number if stored in a non-volatile memory for a long period of time, and thus may become unidentifiable.
Thus, what is needed are improved ways of ensuring that data, such as the identification number, is maintained in a tag for long periods of time, such as for the lifetime of the tag.